A gas turbine engine typically includes a fuel system for delivery of fuel from a fuel source to a combustor where the fuel in combination with compressed air is ignited and produces combustion gases to drive the turbine engine. The fuel is delivered through the system under a fuel pressure established by a fuel pump. When the turbine engine is shut down for any reason, fuel remains in the system. Fuel, particularly liquid fuel, in the fuel system can result in gumming, coking, and similar disadvantageous results, thereby decreasing the operational life of the components, such as fuel nozzles. Furthermore, cold fuel remaining within the fuel system which is not under pressure and is un-metered, can interfere with the next turbine start-up process. The fuel remaining in the system will eventually be lost through leakage from the fuel nozzles, which is not acceptable for ecological reasons and is not effectively used for engine operation. Efforts have been made to find methods of purging fuel from the fuel system on shutdown of the engine. Conventionally, fuel remaining in the system is discharged into the combustor and cannot be reused, or is sucked into an ecology valve cylinder to be stored for re-use in the next engine start-up process but this requires a complicated system structure and compromises the performance reliability of the fuel system and adds weight.
Accordingly, there is a need to provide an improved fuel system of gas turbine engines.